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President Barack Obama endorses Hillary Clinton on the third day of the Democratic National Convention. (Published Thursday, July 28, 2016)

Their political fates now entwined, President Barack Obama implored with voters Wednesday to elect Hillary Clinton, appealing to the women, minorities and young people who powered his rise and are now crucial to hers.

Obama told delegates at the Democratic National Convention in Philadelphia there has never been a man or a woman — "not me, not Bill" — who's more qualified than his former secretary of state to be president of the United States and endorsed her as the woman to finish the job he started eight years ago.

"Nothing truly prepares you for the demands of the Oval Office. Until you've sat at that desk, you don't know what it's like to manage a global crisis, or send young people to war," Obama said. "But Hillary's been in the room and knows what's at stake."

Exactly 12 years to the day after the obscure Senator from Illinois delivered a rousing speech to the Democratic convention, Obama defended his White House legacy and argued that the former secretary of state would be the best choice to bequeath those policies.

Chelsea Clinton Speaks at DNC

Chelsea Clinton Speaks at the Democratic National Convention on Thursday night. (Published Friday, July 29, 2016)

Obama cast Clinton as a candidate who believes in the optimism that fuels the nation's democracy and warned against the "deeply pessimistic" vision of Republican Donald Trump.

"America is already great. America is already strong," he declared to cheering delegates Wednesday night at the Democratic convention. "And I promise you, our strength, our greatness, does not depend on Donald Trump."

In addition to party loyalty, a big motivation for Obama's robust support is deep concern that the Republican nominee can win in November and unravel the president's eight years in office.

Obama acknowledged the economic and security anxieties that have helped fuel Trump's rise, but he argued they don't define the country.

Hillary Clinton Quotes Roosevelt's Fear Speech

Remarking on Donald Trump's reliance on fear, Hillary Clinton quoted President Franklin Delano Roosevelt's famous fear quote that he gave during the throes of the Great Depression. (Published Friday, July 29, 2016)

"Through every victory and every setback, I've insisted that change is never easy, and never quick; that we wouldn't meet all of our challenges in one term, or one presidency, or even in one lifetime," Obama said, adding that he's "more optimistic of the future of America then ever before."

Wednesday night's Democratic lineup was aimed at emphasizing Clinton's own national security credentials, a shift from two nights focused more on re-introducing her to voters as a champion for women's issues, children and families. Among those were former Pentagon and CIA chief Leon Panetta, who served alongside Clinton in Obama's Cabinet.

Panetta, citing his experience working alongside nine U.S. presidents, said he believes, in this election, Hillary Clinton "is the only candidate that has the experience, judgment and temperament to be Commander in Chief."

Obama, too, was vouching for Clinton's national security experience, recalling their work together during trying times and saying she won't relent until ISIL is destroyed.

Clinton on Trump: 'A Man You Can Bait With a Tweet'

In her remarks at the DNC on July 28,2016, Hillary Clinton called her opponent Donald Trump "a man you can bait with a tweet" and "not a man we can trust with nuclear weapons." (Published Friday, July 29, 2016)

"And she'll do it without resorting to torture, or banning entire religions from entering our country," Obama said.

Touting Clinton's experience and judgment, Obama's speech was a direct rebuttal to Trump's attacks on Clinton at last week's Republican convention in Cleveland, when he claimed her tenure as secretary of state was marked by "death, destruction and weakness."

In a statement, Trump's campaign called the Democratic Party "disconnected from what's happening in our world," and said Democrats described a vision of America that "doesn't exist for most Americans."

"They resorted to the politics of fear, trying to convince Americans not to vote for change — they spoke on behalf of the big banks and the big elites, not on behalf of suffering Americans," Trump's campaign said.

Hillary Clinton at Convention: 'Sky's the Limit'

Hillary Clinton notes the historical importance of her nomination to a major political party. (Published Friday, July 29, 2016)